1. Field of the Invention
The invention relates to a driver assistance device for warning a driver of a motor vehicle of a risk of departure from the road or from the lane.
2. Related Art of the Invention
Modern driver assistance devices for warning a driver of a motor vehicle of a risk of departure from the lane or the lane, known as a lane-departure warning system, contribute considerably to increasing road safety through the detection of hazardous situations by outputting acoustic or optical warning signals when there is the risk of departure from the lane or the lane.
Contemporary lane-departure warning systems usually have an image-transmitting sensor for lane detection and lane detection, which sensor is connected to an evaluation device which detects lane markings, edge-of-lane markings and, in some cases, structural boundaries of the edges of the lane as edge-of-lane markings in the area sensed by the image-transmitting sensor. Such lane-departure warning systems typically warn the driver when the motor vehicle enters into contact with or passes beyond the edge-of-lane marking which is detected as the edge of the lane by means of a warning device which is connected to the evaluation device. In such a case, the warning device may both cause a warning signal to be output and bring about an automatic braking or steering intervention.
However, lane-departure warning systems which are equipped with only one image-transmitting sensor are not capable of differentiating between edge-of-lane markings and a structural boundary at the edge of the lane, for example kerb stones, crash barriers or concrete walls so that in particular in sections of a road in which no edge-of-lane markings are provided and a structural boundary forms the edge of the lane these do not reliably and adequately warn of a risk of departure of the motor vehicle from the lane. If, for example, a kerb is detected by such a lane-departure warning system as an edge-of-lane marking, damage to the tyres or the rims of the motor vehicle already occurs if a warning of a risk of departure of the motor vehicle from the lane is not issued until the motor vehicle enters into contact with or passes beyond the supposed marking. This damage and the associated hazard situation, together with the resulting loss of confidence of the driver of the motor vehicle in the reliability of the lane-departure warning system, have an adverse effect on the road safety of the motor vehicle. Furthermore, as a result of faults in the evaluation of the data supplied by the image-transmitting sensor incorrect warnings may easily occur, in particular in regions without edge-of-lane markings.
Furthermore, driver assistance devices are known which have at least two forwardly directed, image-transmitting sensors with which distances can be measured in particular from vehicles travelling ahead or from objects on the lane, in particular so that a vehicle travelling ahead can be followed at a constant distance, or so that, if appropriate, collision prevention measures can be taken by observing the change in the distance. Such driver assistance devices are known, for example, as Adaptive Cruise Control, abbreviated to ACC. The image-transmitting sensors of such ACCs are basically also suitable for detecting the lane markings or edge-of-lane markings, with a reliable distinction between a structural boundary of the edge of the lane and an edge-of-lane marking being impossible owing to the viewing direction of the forwardly directed image-transmitting.
DE 37 38 221 A1 discloses a method and a device for detecting the state of a road, in particular unevennesses on the surface and the edge of a lane, using electromagnetic waves such as light, according to the principle of transit time measurement, with a transmitter emitting measurement beams and a receiver receiving reflected measurement beams which produce signals which are to be evaluated on reception. In this context, by splitting the reflection into component surfaces the useful signal is separated and evaluated by forming differences between the respective transit times of the back-scattering to the receiver. The intention is that, by evaluating the differences between the back-scattered signals of a plurality of transmitters and receivers, a geometric relationship between the change in the signals, and thus also the edge of the lane, is to be formed so that unevennesses on the lane can be differentiated from those at the edge of the lane in order to set chassis properties such as, for example, damper response behaviour to the unevennesses detected on the surface of the lane.
EP 1 245 443 A2 has disclosed a driver assistance device for early detection of possible collisions of a motor vehicle, in particular with animals such as elks or bears, in which forwardly directed, image-transmitting sensors are used to determine the position and the distance from an object and the relative velocity between the motor vehicle and the object, and to acquire the probability of a collision therefrom, on the premise that the relative velocity is near to the motor vehicle's own velocity. The image-transmitting sensors are provided here for sensing objects which are located at a large distance ahead of the motor vehicle.
WO 00/77736 discloses a method for detecting objects in the surroundings of a road vehicle up to large distances, in which method the distance between a moving vehicle or stationary vehicle and one or more objects is calculated by distance-based image segmentation by means of stereo image processing, and properties of the detected objects are acquired by object detection in the segmented image areas. Image areas of elevated objects and/or flat objects are acquired and elevated objects and/or flat objects are detected by combining 3D points according to predetermined criteria, with elevated objects being determined by means of features with similar distance values, and flat objects by means of features with similar height values. As a result, other vehicles, for example parked vehicles, guideposts, bridge pillars, and lampposts can be differentiated from structural lane boundaries such as for example kerb or crash barriers.
DE 199 49 409 A1 discloses a method and a device for detecting objects having at least two distance-resolving sensors which are mounted on a motor vehicle and whose detection ranges at least partially overlap, with the relative positions of possible detected objects with respect to the sensors being determined using the triangulation principle in the overlapping region, and possible virtual objects, which arise as a result of the determination of objects, being acquired by means of dynamic consideration of objects. In this context, objects can be detected only within the overlapping region located in front of the vehicle in its direction of travel.
DE 102 60 855 A1 discloses a method for detecting object configurations by means of distance signals of at least two sensors, in which method the distance signals of a plurality of the sensors are subjected to a pattern detection by comparison with reference patterns which correspond to predefined model configurations. The method is provided for use in conjunction with ACCs, with motor vehicles which are travelling ahead being characterized by reflection points which remain the same in relation to one another on a group basis, and being detected as such by comparison with reference patterns so that of the plurality of reflection points which represent a motor vehicle that has been detected it is possible to consider exclusively the reflection point which is at the shortest distance from the actual motor vehicle in order to prevent a collision.
WO 2004/055547 A1 discloses a method and a device for detecting objects with vehicle-bound sensors whose sensing ranges overlap at least partially. In this context, signals from at least two sensors with essentially congruent sensing ranges and additional signals of a further sensor whose sensing range overlaps only partially with the sensing ranges of the other sensors are evaluated. An object is detected as relevant if it is detected by at least two sensors. This information is provided for further processing in an ACC, with relevant objects being motor vehicles which are located ahead of the actual vehicle on the same lane or an adjacent lane.
DE 101 14 932 A1 discloses carrying out three-dimensional sensing of the surroundings of the motor vehicle, for example in order to detect a parking space, by means of a distance sensor which emits radiation in one plane and is arranged on a motor vehicle, by recording the distance profiles during the movement of the motor vehicle. In this context, a three-dimensional image of the surroundings is generated by means of a distance sensor which generates a two-dimensional distance profile, and from a data processing means and a storage unit which processes successive distance profiles and stores them, and from a concatenation of a set of successive distance profiles.
According to the prior art, it is consequently not known to differentiate a structural boundary of the edge of the lane from an edge-of-lane marking by means of suitable sensors and to use this information to improve the method of operation of a lane-departure warning system.